Jump to content

marvel carb help


Recommended Posts

I have a marvel carb on my '30 buick. I just put a 6volt fuel pump on and my carb. it is not functioning right. It will idle fine but when i give it some gas the car seems to loose power. I think the carb is really worn. I know it needs attention and probably new jet valves. Does anyone know of someone that complete rebuildes these type of carbs. or does someone recommend another carb to put on the car?

Link to post
Share on other sites

There is not much to these Marvel updraft carburators, a few jets and a spring loaded flapper valve that opens the throat of the carb as the engine speeds up. This is also an enrichment jet that is tied to the throttle and richens the mixture under load, like a power valve in a modern carb.

Start by cleaning the unit to make sure all the jets are open. Blow carb cleaner through all the jet passages. Make sure that flapper can move smoothly. It is tied to that major brass thumbwheel with a calibrated spring. My 1927 Marvel has only two adjustable items, the thumbsheel on the flapper valve and the main needle jet on the bottom of the carburator. Yours may have a separate idle needle. Mine requires adjustment between that main needle and the thumbwheel to get good running at low and high speeds.

The Marvel is frequently attacked, it is not the greatest carburator ever built. If I set mine for good high speed running, the idle is a bit too rich. But it is simple, and a decent mechanic who knows carburators should have little trouble getting it to work -- unless it has fractured parts inside. The insides are made mostly of brass and you should not need a carburator kit to clean it, though you may have to make a gasket or two. It is not much different what you might find on a lawn mower.

Some folks replace them with an updraft Stromberg and report that they work a lot better. More radical is to flip the intake manifold over and put a modern downdraft unit on the car. This can work well but looks ugly and takes a lot of mods to make it happen.

We like our Marvel, it has its quirks, but car starts right up and probably runs like the car did when it was new!

Bill.

Link to post
Share on other sites

Does it blow black smoke when you accelerate???

I tried an electric pump on my 30 and like you found it idled well but under acceleration lost power. It was getting way to much fuel ( the black smoke is a good indicator of this, plus the loss of power ) and I couldnt reduce the pressure on the electric pump ( although I am told there are simple inexpensive devices which do this ).

My solution was to buy a fuel pump overhaul kit for the original mechanical pump ( from Bob's ), it's an easy rebuild and I haven't had any problem since ( 10 years and 15000 miles ).

Link to post
Share on other sites

These are all good suggestions. You should also check to make sure the heat riser tube is not leaking exhaust into the intake. Remove and inspect the inside tube for rust or cracks. Any leaks would cause your symptoms.

Link to post
Share on other sites

I have a 30 Buick Business coupe with the same carb. My car would hardly run with the carb as it was. I sent it to a guy called "The Old Carb Doc" in North Carolina (Jeff Dreibus). He was reasonable and did a great job. Having the carb rebuilt made all the difference in the world. He made a slight modification to the carb which may be recommended if you drive the car a lot like I do. He refitted the carb to use Quadra Jet needle valve and seat which is a rubber tipped needle valve. He says that the carb works much better with this mod which no one will know about except you. The brass needle valve and seat must be matched and ususally leak anyway.

You will probably need to give the old carburetor heat system looked at, too. Mine leaked and I ended up pulling out the old leaky sleeve and sealing off the port where the exhaust gasses entered. You don't need the carb heat with modern fuels and the orignal system causes lots of troubles (as others have told me). Removing the sleeve is kind of a call on your part. I could not find a new one and removing the restriction seemed to have given me much more power. It wasn't without a cost, however, as now I have to run with the choke pulled out a little and I'm sure my lousy fuel economy is even worse now (8 to 10 mpg).

Link to post
Share on other sites

yes it does smoke black . One thing that I noticed is that when I try to start the car, it takes longer now. rolls over and over and finally fires. I feel like that carb is either way to rich or way to lean. no happy medium. I now srew my air intake all the way in to get it to idle at all. If i back it out it kills the car.

Link to post
Share on other sites

Really does sound like the electric pump pressure is too high and having the carb rebuilt won't rectify that problem.

Mark raises a good point about the heat riser tube and that should be checked for leaks either by way of cracks in the outer casting or the tube itself being rusted out. My experience with that problem is it actually suffocates the motor with exhaust gases and it stops completely when you accelerate. This is probably dependant on how large the crack is or how badly rusted out the heat riser tube is.

The carb is really very simple and you could put a kit through it yourself ( available again from Bob ). It also seems the air control spring is pretty critical and I have read that this should not be tampered with i.e. stretching or compresing.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...